1. Field of the Invention
The present invention relates to a liquid crystal display device including a reflector, and a portable electronic apparatus. More particularly, the present invention relates to a liquid crystal display device which has a viewing angle property that allows a display to appear brighter when a viewer looks at the display from a direction close to a direction of a normal line with respect to a display surface of the liquid crystal display device than when the viewer looks at the display from other viewing angles; and a portable electronic apparatus including at its display section the liquid crystal display device with such a viewing angle property.
2. Description of the Related Art
In general, liquid crystal display devices are called semi-transmissive liquid crystal display devices or transmissive liquid crystal display devices, which include backlights, or reflective liquid crystal display devices, depending upon the form of display of the liquid crystal display devices. To display images, reflective liquid crystal display devices use only outside light, such as sunlight or light from indoor illumination sources, and, thus, do not use a backlight. Reflective liquid crystal display devices are frequently used in, for example, portable information terminals that are under constant stress to be made thinner and lighter and to have decreasing power consumption.
When semi-transmissive liquid crystal display devices are in an environment that does not provided sufficient outside light, a backlight is turned on for operation in a transmission mode. On the other hand, when semi-transmissive liquid crystal display devices are in an environment that provides sufficient outside light, the backlight is not turned on, so that they operate in a reflection mode thereby saving power. Semi-transmissive liquid crystal display devices are frequently used in portable electronic apparatuses, such as cellular phones or notebook-size personal computers (PC).
FIG. 12 is a sectional view of an example of a related transflective liquid crystal display device.
In the general structure of the transflective liquid crystal display device, a reflection mode STN (super-twisted nematic) liquid crystal cell 72, a forward scattering plate 90, an upper retardation plate 73b, and an upper polarizing plate 74 are placed upon each other on a lower retardation plate 73a of a reflective plate 71 in that order from the side of the lower retardation plate 73a; and a backlight 95, serving as a light source, is provided below the reflective plate 71. The reflective plate 71 has a lower polarizing plate 70 and the lower retardation plate 73a provided thereat.
In the general structure of the liquid crystal cell 72, a lower glass substrate 75, a color filter 76, a lower transparent electrode layer 78, a lower alignment film 79, an upper alignment film 80 disposed so as to be separated from and to oppose the lower alignment film 79, an upper transparent electrode layer 81, and an upper glass substrate 82 are placed upon each other in that order from the side of the lower polarizing plate 70. A super-twisted nematic liquid crystal layer 83 is disposed between the lower and upper alignment films 79 and 80. An overcoat layer (not shown), formed of silica or acrylic resin, is provided between the color filter 76 and the lower transparent electrode layer 78.
The reflective plate 71 has an Al film whose surface is in a specular state, and has holes 71a for passing light from the backlight 95 when the backlight 95 is used.
The retardation plates 73a and 73b are provided to prevent coloring of the display into blue or yellow by compensating for phase differences of light that passes through the STN liquid crystals.
The forward scattering plate 90 is causes the incident light to be reflected not only in a specular reflection direction by the surface of the reflective plate 71, but also in a direction close to the specular reflection direction by the surface of the reflector 71. The forward scattering plate 90 achieves this by scattering light (outside light) passing through the upper polarizing plate 74 and the upper retardation plate 73b and incident upon the forward scattering plate 90 towards the liquid crystal cell 72.
FIG. 13 illustrates another example of a related transflective liquid crystal display device.
In the general structure of the transflective liquid crystal display device, a first retardation plate 173a, a second retardation plate 173b, and a polarizing plate 174 are placed upon each other on a reflection mode STN (super-twisted nematic) liquid crystal cell 172 in that order from the side of an upper glass substrate 182; and a backlight 195, serving as a light source, is provided below the liquid crystal cell 172.
In the general structure of the liquid crystal cell 172, a lower glass substrate 175, a reflector 171, an overcoat layer 171c, a color filter 176, an overcoat layer 177a, a lower transparent electrode layer 178, a lower alignment film 179, an upper alignment film 180 disposed so as to be separated from and to oppose the lower alignment film 179, a topcoat layer 177b, an upper transparent electrode layer 181, and an upper glass substrate 182 are placed upon each other in that order.
Many minute bumpy portions (recesses 171e in FIG. 13) are formed adjacent each other in an irregular manner at a reflective surface of the reflector 171. The bumpy portions can be formed by, for example, conventional photolithography methods. In one such method, a surface of a resin base material 171a, such as a photosensitive resin layer, is irradiated with light through a mask pattern, the exposed resin is developed to form many minute adjacent spherical recesses, and the surface of the resin base material 171a having the spherical recesses is subjected to evaporation or plating using, for example, aluminum or silver in order to form a metallic film 171b having the bumpy portions (the recesses 171e).
The metallic film 171b can be made thin (to a thickness of the order of 30 nm) so that light from the backlight 195 can pass therethrough when the transflective liquid crystal display device is in a transmission mode.
The inside surfaces of the recesses 171e are spherical, and have an inclination angle distribution in a range of from xe2x88x9220 degrees to +20 degrees and a depth within a range of from 0.1 xcexcm to 3 xcexcm. Distances between the recesses 171e are set so that pitches between adjacent recesses (center-to-center distance) differ within a range of from 5 xcexcm to 50 xcexcm.
To achieve satisfactory display performance of a liquid crystal display device, it is ordinarily necessary for factors such as (1) resolution, (2) contrast, (3) brightness of a screen, (4) brightness of color, and (5) visibility (viewing angle wideness) to be satisfactory.
As shown in FIG. 14, a liquid crystal display device which is incorporated in an apparatus which is used with its display surface inclined, such as a portable information terminal including a cellular phone or a notebook-size personal computer, is frequently viewed from a direction close to a normal line direction P with respect to the display surface. More particularly, the information terminal is frequently viewed from a direction within a range of about 10 degrees from the normal line direction P. In general, an angle xcex8 between a main viewing direction xcex1 when a viewer (user) views the display surface (screen) and the normal line direction P is frequently within a range of from about 0 degrees to about 20 degrees.
FIG. 14 illustrates a state in which a cellular phone including a display section 100 which comprises a liquid crystal display device and which is provided in a body 105 is being used. In FIG. 14, reference character P denotes the normal line with respect to the display surface of the display section 100, reference character Q denotes incident light, and reference character xcfx89o denotes an incidence angle (such as about 30 degrees) of the incident light from the normal line. Reference character R1 denotes reflected light (specularly reflected light) when the incidence angle xcfx89o and a reflection angle xcfx89o are equal from the normal line, reference character R2 denotes reflected light when the reflection angle xcfx89 is smaller than the incidence angle xcfx89o from the normal line, and reference character R3 denotes reflected light when the reflection angle xcfx89o is greater than the incidence angle xcfx89o from the normal line.
As can be seen from FIG. 14, a viewing point Ob of the viewer is concentrated ordinarily in the reflected-light-R2 direction close to the normal line direction P, specifically, in a direction within a range of up to about 10 degrees from the normal line direction P. In contrast, the reflected light beams R1 and R3 are such as to cause the viewer to look at the display surface from the lower side to the upper side, thereby making it difficult for the viewer to see what is displayed on the display surface. Therefore, it is desirable to provide a wide viewing angle and, at the same time, to increase the reflection ratio of the liquid crystal display device in a direction where the reflection angle is smaller than a specular reflection angle.
However, when the related liquid crystal display device shown in FIG. 12 is in a reflection mode, the range in which incident light is reflected is wider than that of a liquid crystal display device of the type that does not include a forward scattering plate, but most of the incident light is reflected in the specular reflection direction and in directions near the specular reflection direction (reflection ratio peak value occurs at a specular reflection angle or at angles close to the specular reflection angle). Therefore, when the viewer views the display section from the specular reflection direction and in directions close to the specular reflection direction, what is displayed on the display section appears bright. However, when the viewer views it from other directions, what is displayed on the display section appears dark.
In the related liquid crystal display device shown in FIG. 13, a large portion of the incident light is reflected in the specular reflection direction and in directions close to the specular reflection direction (peak value of the reflection ratio occurs at the specular reflection angle or at angles that are slightly greater than or less than the specular reflection angle). Therefore, when the viewer views the display section from the specular reflection direction and from directions close to the specular reflection direction, what is displayed on the display section appears bright. However, when the viewer views it from other directions, what is displayed on the display section appears dark.
Accordingly, since, as mentioned above, the viewing point of the viewer is ordinarily concentrated in directions close to the normal line direction P when the display surface of, for example, a cellular phone including any one of the related transflective display devices at the display section is viewed, the display appears dark. When the viewer tries to view the display so that it appears bright, the viewer must view the display from the specular reflection direction or directions close to the specular reflection direction, in which case, as mentioned above, the viewer views the display surface upward from the lower side to the upper side, thereby making it difficult to see what is displayed on the display section. Thus, typical users require not only a broader range of viewing angles (with sufficient brightness), but also increased brightness specifically at a range of typically used viewing angles (relatively close to the normal line of the display) than that provided from conventional displays.
The present invention has been achieved to overcome the above-described problems. It is a first object of the present invention to provide a liquid crystal display device which has a viewing angle property that allows a display to appear brighter when a viewer looks at a display surface of the liquid crystal display device from a direction close to a direction of a normal line with respect to the display surface than when the viewer looks at the display surface from other viewing angles.
It is a second object of the present invention to provide a portable electronic apparatus, such as portable electronic terminals including a cellular phone or a notebook-size personal computer, including at its display section the liquid crystal display device having a property such as that mentioned above.
To achieve the first object, according to a first aspect of the present invention, there is provided a liquid crystal display device including a reflector disposed at an outside surface side of a first substrate of a liquid crystal cell or between the first substrate and an electrode disposed at an inside surface side of the first substrate. The liquid crystal cell is formed by providing the electrode and an alignment film at the inside surface side of the first substrate in that order from a side of the first substrate and by providing an electrode and an alignment layer at an inside surface side of a second substrate in that order from a side of the second substrate, with the first substrate and the second substrate opposing each other so as to sandwich a liquid crystal layer. In the liquid crystal display device, a retardation plate and a polarizing plate are provided at an outside surface side of the second substrate in that order from the side of the second substrate. When an angle between a direction of a normal line with respect to a display surface of the liquid crystal display device and a main viewing direction is from 0 degrees to about 20 degrees, a reflection ratio peak value of light incident upon the liquid crystal display device and reflected by the reflector is set so as to occur within a range of about 30 degrees from the normal line direction.
According to the liquid crystal display device of the present invention having such a structure, the amount of light reflected within the range of about 30 degrees from the direction of the normal line with respect to the display surface of the liquid crystal display device becomes large, so that distribution of the amount of reflected light in directions close to a viewing point of a viewer becomes large. At a practical viewing point, particularly at angles of 0 to about 20 degrees between the normal line direction and the main viewing direction, the liquid crystal display device can provide a bright display (screen).
When the structure of the first aspect is used, the reflection ratio peak value of the light incident upon the liquid crystal display device and reflected by the reflector may be set so as to occur within a range of about 20 degrees from the normal line direction.
According to the liquid crystal display device of the present invention having such a structure, the amount of light reflected within the range of about 20 degrees from the direction of the normal line with respect to the display surface of the liquid crystal display device becomes large, so that the distribution of the amount of reflected light in directions close to the viewing point of the viewer becomes large, as a result of which an area where the amount of reflected light is large is widened. At a practical viewing point, particularly at angles of 0 to about 20 degrees between the normal line direction and the main viewing direction, the liquid crystal display device can provide a bright display (screen).
When the structure of the first aspect is used, the reflector may include a plurality of recesses with light reflectivity formed in a surface of a base material or a metallic film formed on the base material. Here, the recesses have inside surfaces which form parts of spherical surfaces, and have an inclination angle distribution in a range of from xe2x88x92about 30 degrees to +about 30 degrees. The recesses are formed irregularly so as to have depths within a range of from 0.1 xcexcm to 3 xcexcm. The recesses are disposed irregularly so that pitches between adjacent recesses are in a range of from 5 xcexcm to 50 xcexcm.
The liquid crystal display device may have a reflection ratio peak value substantially constant between a range of about 10 degrees to about 50 degrees or about 20 degrees to about 40 degrees from the normal line direction. The reflection ratio peak value may be substantially constant over a range of not less than about 10 degrees.
To achieve the first object, according to a second aspect of the present invention, there is provided a liquid crystal display device including a reflector disposed at an outside surface side of a first substrate of a liquid crystal cell or between the first substrate and an electrode disposed at an inside surface side of the first substrate. The liquid crystal cell is formed by providing the electrode and an alignment film at the inside surface side of the first substrate in that order from a side of the first substrate and by providing an electrode and an alignment layer at an inside surface side of a second substrate in that order from a side of the second substrate, with the first substrate and the second substrate opposing each other so as to sandwich a liquid crystal layer. In the liquid crystal display device, a retardation plate and a polarizing plate are provided at an outside surface side of the second substrate in that order from the side of the second substrate. When an angle between a direction of a normal line with respect to a display surface of the liquid crystal display device and a main viewing direction is from 0 degrees to about 20 degrees, a reflection ratio peak value of light incident upon the liquid crystal display device and reflected by the reflector is set so as to occur within a range of angles less than about 30 degrees from the normal line direction.
According to the liquid crystal display device having such a structure, the amount of light reflected within the range of angles less than about 30 degrees from the direction of the normal line with respect to the display surface of the liquid crystal display device becomes large, so that distribution of the amount of reflected light in directions close to a viewing point of a viewer becomes large. At a practical viewing point, particularly at angles of 0 to about 20 degrees between the normal line direction and the main viewing direction, the liquid crystal display device can provide a bright display (screen).
When the structure of the second aspect is used, the reflection ratio peak value of the light incident upon the liquid crystal display device and reflected by the reflector may be set so as to occur within a range of about 20 degrees from the normal line direction.
According to the liquid crystal display device of the present invention having such a structure, the amount of light reflected within the range of about 20 degrees from the direction of the normal line with respect to the display surface of the liquid crystal display device becomes large, so that the distribution of the amount of reflected light in directions close to the viewing point of the viewer becomes large, as a result of which an area where the amount of reflected light is large is widened. At a practical viewing point, particularly at angles of 0 to about 20 degrees between the normal line direction and the main viewing direction, the liquid crystal display device can provide a bright display (screen).
When the structure of the second aspect is used, the reflector may include a plurality of recesses with light reflectivity formed in a surface of a base material or a metallic film formed on the base material. Here, each of the recesses is formed so that an inclination angle (absolute value of an angle between the base material surface and a tangential plane at any point on a curvature) at each one of a corresponding side portion becomes a maximum. The recesses are formed irregularly so as to have depths within a range of from 0.1 xcexcm to 3 xcexcm. The recesses are irregularly disposed so that pitches between adjacent recesses are in a range of from 5 xcexcm to 50 xcexcm.
When the structure of the first aspect is used, a thickness of a metallic film when the reflector includes a base material and the metallic film having a plurality of recesses and formed on the base material may be in a range of from 8 nm to 20 nm. Therefore, the metallic film becomes thin, so that transmittancy with respect to light from a backlight disposed below the reflector can be increased, thereby making it possible to use the liquid crystal display device as a transflective liquid crystal display device exhibiting excellent properties when light is reflected and when light is transmitted. When the reflector is formed of a base material having a plurality of recesses, the thickness of the base material is made to lie within the range of from 8 nm to 20 nm, so that the base material becomes thin, and, thus, the transmittancy with respect to the light from the backlight disposed below the reflector can be increased. Therefore, it is possible to use the liquid crystal display device as a transflective liquid crystal display device exhibiting excellent properties when light is reflected and when light is transmitted.
To achieve the second object, according to a third aspect of the present invention, there is provided a portable electronic apparatus including at a display section thereof the liquid crystal display device having the structure of the first aspect.
When such a portable electronic apparatus of the present invention having such a structure is used, a portable electronic apparatus, such as a cellular phone or a notebook-size personal computer, having a display surface (screen) with excellent visibility in a reflection mode of operation or in either the reflection mode or a transmission mode of operation can be provided.
The liquid crystal display device may have a reflection ratio peak value substantially constant between a range of about 20 degrees to about 30 degrees or about 10 degrees to about 25 degrees from the normal line direction. A center of the reflection ratio peak value area may be approximately 25 degrees or approximately 15 degrees.
The reflector may include a plurality of aspherical recesses with light reflectivity formed in a surface of a base material or a metallic film formed on the base material. Each of the recesses may have a maximum inclination angle (an absolute value of an angle between a surface of the base material and a tangential plane at any point on a curvature) that differ irregularly and have values within a range of from about 2 degrees to about 90 degrees, may be formed irregularly and have depths (a distance between a minimum point of each recess and the surface of the base material) within a range of from about 0.1 xcexcm to about 3 xcexcm, and may be disposed irregularly such that pitches between adjacent recesses are in a range of from about 5 xcexcm to about 50 xcexcm. The maximum inclination angles of a majority of the recesses may have values within a range of from about 4 degrees to about 35 degrees. The recesses may have a single minimum point.
The liquid crystal display device may have a reflection ratio peak value substantially constant over a range of not less than about 10 degrees.
Another embodiment that achieves the above objectives is a method of improving viewing of a liquid crystal display device having a reflector and a display surface. The method comprises setting a reflection ratio peak value of light incident upon the liquid crystal display device and reflected by the reflector to occur within a range of less than about 20 degrees from a direction of a normal line with respect to the display surface when an angle between the normal line direction and a main viewing direction of the display surface is about 0 degrees to about 20 degrees and broadening the reflection ratio peak value to be substantially constant over a range of not less than about 10 degrees.
The method may further comprise providing a plurality of asymmetric recesses in the reflector. The method may further comprise providing a thickness of material in which the recesses are formed in a range of from about 8 nm to about 20 nm. Further, the method may further comprise providing recesses: that have a maximum inclination angle (an absolute value of an angle between a surface of material in which the recesses are formed and a tangential plane at any point on a curvature) that differs irregularly and has a value within a range of from about 2 degrees to about 90 degrees, that are formed irregularly and have depths (a distance between a minimum point of each recess and the surface of the base material) within a range of from about 0.1 xcexcm to about 3 xcexcm, and that are disposed irregularly such that pitches between adjacent recesses are in a range of from about 5 xcexcm to about 50 xcexcm.
In addition, the method may further comprise providing recesses in which the maximum inclination angles of a majority of the recesses have values within a range of from about 4 degrees to about 35 degrees or providing recesses that have a single minimum point.